Rare earth containing P2O5-WO3-Na2O glass for laser applications

ABSTRACT

A rare earth containing glass nominally based on the ternary P 2 O 5  —WO 3 —Na 2 O—Ln 2 O 3  compositional space, with WO 3 &gt;30-65 mole %, Na 2 O 15-35 mole %, P 2 O 5  5-65 mole %, Ln 2 O 3  (Ln=one or more cations selected from lanthanum or any of the rare earth oxides) up to the limit of solubility; with optional additives, MoO 3  being a preferred additive, that can be employed alone or in combination at levels up to 15 mole %.

[0001] The glasses of the present invention are useful as activematerials for generation and/or amplification of optical laserradiation. They are advantageously employed as sources or amplifyingmedium of light when doped with suitable active rare earth cations. Theyare particularly advantageously employed as sources or amplifying mediumin telecommunications applications where they are doped with lanthamidecations, preferably with erbium cations, alone or in combination withytterbium cations. When employed in this manner, the glasses of thepresent invention offer a lasing range that is broader, and more flat(uniform) in its gain, than the conventional erbium doped phosphate gainmaterial commonly employed today. The glasses of this invention can beprepared in bulk or fiber form, and are structurable by conventionaltechniques such as ion exchange, allowing the preparation of planar andfiber waveguide structures that can be employed as these gain media.

[0002] The use of the glasses according to the invention enables small,compact amplifiers to be constructed from either fibers or planarwaveguides that offer flat (uniform) amplification over an increasedwavelength range compared to the currently existing EDFA for applicationto the C-band telecommunications wavelength region (from 1530 to 1562nm) as well as for the L-band region (1570 to 1610 nm) that is expectedto be employed in the future as there continues to be increasedrequirements for increased bandwidth.

[0003] In addition, glasses with broad emission are known to offer thepotential to construct laser systems that operate with extremely shortpulse lengths, less than 1 nsec or even shorter, e.g., at less than 1psec or less than 500 fsec.

[0004] In one aspect, the invention relates to rare earth, Ln, dopedglasses prepared within the ternary P₂O₅—WO₃—Na₂O compositional space,with WO₃>30-65 mole %, preferably 50-60 mole %, more preferably about 55mole %; Na₂O 5-35 mole %, preferably 15-25 mole %; P₂O₅ 5-65 mole %,preferably >15-65 mole %, e.g., 16-, 17-, 18-, 19-65 mole %, morepreferably 20-30 mole %, that are also doped with Ln₂O₃ (where Ln refersto one or more cations selected from lanthanum or any of the rare earthoxides) at a content level up to the limit of solubility in the glass,preferably in the range of 0.01 to 2.0 mole %, more preferably 0.1-1.5mole %, and even more preferably in the range of 0.2-0.4 mole %; withother optional additives such as MoO₃, Nb₂O₅, TiO₂, B₂O₃, Ga₂O₃, Sb₂O₃,BaO, Bi₂O₃, SnO₂, Y₂O₃, ZrO₂, TaO₅, In₂O₃, MO, and/or R₂O, wherein R isLi or K with or without the presence of another alkali, or is at leasttwo elements selected from the group consisting of Li, Na, K, Rb, Cs,Ag, and Tl, and M is Mg, Ca, Sr or Zn; preferably MoO₃, that can beemployed alone or in combination with other additives at levelspreferably up to 15 mole %, preferably at levels below 10 mole %, e.g.,for example for TeO₂, more preferably up to about 5 mole %, that mayenhance the gain characteristics for particular applications, improvemeltability and/or resultant optical quality of produced glass, andincrease solubility for rare earth ions. MoO₃ can be advantageouslyincluded at levels of about 10 mole %. TeO2 affects the bandwidth ofglasses. The glasses of the present invention offer increased crosssection for stimulated emission and broader emission bandwidth comparedto state of the art phosphate glass.

[0005] It is within the scope of the invention to batch the glasses withfluoride, carbonate, nitrate, and/or chloride compounds instead of, orin combination with, the oxide compounds. In each case when other thanoxides are used to batch the glasses, enough material is input to beequivalent to the needed oxide amount.

[0006] The glasses of the present invention can be doped with rare earthoxides, including, but not limited to La, Ce, Pr, Nd, Sm, Eu, Gd, Tb,Dy, Ho, Pm, Lu, Tm, Er and/or Yb, preferably with Nd, Pr, Dy, Tm, Er,and/or, Yb, more preferably with Er, Yb, and/or Nd. Preferred ranges forEr are 0.01 to 0.40 mole %, more preferably 0.15-0.35 mole %, and evenmore preferably about 0.28-0.32 mole %. Preferred ranges for Yb are0.1-1.4 mole %, more preferably about 0.3-1.2 mole %. Preferred rangesfor Nd are 0.01-1.4, more preferably 0.3 to 1.2 mole %. These rare earthoxides can be employed alone or in combination of one or more in orderto take advantage of other available lasing wavelengths andsensitization or up conversion schemes for generating or amplifyinglight at various wavelengths. Examples include Nd at nominally 0.9 μM,1.0 μm, and 1.3 μM, Yb at nominally 1.0 μm, Tm at 1.4 and 2.0 μg, Dy at1.3 μg, and Er at wavelengths other than 1.54 μm, for example Er at 2.9μm.

[0007] In another aspect, the invention relates to the glass familybased on P₂O₅—WO₃—MO₃—Na₂O as a rare earth containing, structurable,laser glass to offer broad emission bandwidth for 1.54 μM radiation whendoped with Ln ions, for example, erbium cations.

[0008] The glasses according to the invention offer a) a broaderemission bandwidth compared to the state of the art erbium dopedphosphate glass, b) a flatter gain curve compared to the state of theart erbium doped phosphate material, and c) structurability by ionexchange in a molten salt bath.

[0009] The glasses of the present invention are also useful asupconversion materials such as disclosed in JPH3-295828, and as anonlinear optical medium for applications such as optical switches asdisclosed in J. Am. Ceram. Soc. 85[5] 1083-1088 (2002). The low meltingtemperatures and high thermal expansion values of the glasses of thisinvention may make them attractive for non-optical applications such assoldering (joining) and sealing with high expansion glasses, metals andalloys, and encapsulation of electronic components without thermaldamage.

[0010] In another aspect, the invention relates to a hybrid structure ofone or more materials in which one or more of the materials is/are aglass of the present invention. For example, hybrid structures can becreated by bonding the glasses of this invention to other materials,including but not limited to variants of the glasses of this inventioncontaining no active ions. Further examples include bonding of theglasses of this invention to each other (for example a glass containingerbium and/or ytterbium to a glass containing another rare earth cationsuch as thulium, dysprosium or neodymium), or to other optical materialssuch as glasses and/or crystals, for example, lithium niobate, lithiumtantalate, or other crystals, or even to other materials or componentssuch as semiconductor materials and actual semiconductor laser diodes.In this way, multiple optical functionalites can be combined into asingle structure, increasing integration of multiple optical functionsinto a small package. For example, it becomes possible in a singlepackage to combine: multiple laser sources or amplifiers each operatingat a different power level or wavelength, the excitation or pump laserwith the amplifiers or source lasers, and/or the source lasers oramplifiers with frequency conversion or frequency and amplitudemodulation elements.

[0011] Upon further study of the specification and appended claims,further objects and advantages of this invention will become-apparent tothose skilled in the art.

[0012] The maximum rare earth content (Ln) of these glasses, due tosolubility issues, appears to be about 2×10²⁰ Ln/cm³, however, higherconcentrations, if successfully incorporated into the glasses, arewithin the scope of the invention. The Ln/cm³ value is a calculatedvalue based on the mole % Ln in the glass composition. First, the weight% composition of Ln is calculated from the mole % composition, followedby calculating the number of ions/cm³ based on an assumed density of theglass. It is to be noted that the mole % of compounds in the glasscompositions need not add up to a total of 100 mole % each time, as canbe seen in some of the examples later in this application. In this art,deviations from compositions having 100 mole % material are common andwell understood by those of ordinary skill.

[0013] Without further elaboration, it is believed that one skilled inthe art can, using the preceding description, utilize the presentinvention to its fullest extent. The following preferred specificembodiments are, therefore, to be construed as merely illustrative, andnot limitative of the remainder of the disclosure in any way whatsoever.

[0014] In the foregoing and in the following examples, all temperaturesare set forth uncorrected in degrees Celsius and, all parts andpercentages are by mol, unless otherwise indicated.

EXAMPLES

[0015] The examples were all prepared from the general heavy metal oxidesystem based on P₂O₅—WO₃—MoO₃—Na₂O with a number of additionaladditives, including Ln₂O₃. Initial melts, summarized in Table 1, wereselected to offer acceptable glass forming stability with a maximum(WO₃+MoO₃)/P₂O₅ ratio in combination with a Na₂O level that would bemore than sufficient for ion exchange process ability (i.e. nominally 10to 25 mole %), while batching WO₃ into the glass composition. TABLE 1Initial P₂O₅—WO₃—MoO₃—Na₂O Glass Melting without Ln₂O₃ Oxide PWD-78PWD-85 Na₂O 25 25 WO₃ 55 40 MoO₃ 20 P₂O₅ 20 15

[0016] Rare earth incorporation was completed in the melts presented inTable 2. All Rare earth containing glasses exhibited decreasing opticalquality with increasing rare earth input. Analysis of several castingsindicated that the crystals within each casting were enriched in Yb, Er,and P, as well as depleted in W, compared to the surrounding base glass.SEM and XRD analysis of crystals in many of these melts determined thecomposition to be a rare earth orthophosphate. These orthophosphates areof interest in identifying glass ceramic materials of high transparencycontaining a Ln(PO₄) crystal phase. TABLE 2 Rare Earth Doping ofP₂O₅—WO₃—Na₂O Oxide PWD-83 PWD-83/2 PWD-108 PWD-109 PWD-110 PWD-111PWD-112 PWD-113 Na₂O 23.79 23.48 10 10 10 25 25 15 Er₂O₃ 0.24 0.3 0.320.31 0.29 0.3 0.31 Yb₂O₃ 0.97 1.21 1.26 1.25 — Nd₂O₃ — — — — — — — — WO₃55 55 55 55 55 40 55 45 MoO₃ 10 10 10 20 — 20 P₂O₅ 20 20 25 25 25 15 2020 Oxide PWD-114 PWD-115 PWD-116 PWD-121 PWD-122 PWD-123 PWD-142 Na₂O 1525 25 15 25 25 20 Er₂O₃ 0.32 0.3 0.3 0.31 0.3 — Yb₂O₃ — 1.21 0.6 — 0.290.3 — Nd₂O₃ — — — — — — 0.27 WO₃ 60 55 55 55 55 55 55 P₂O₅ 25 20 20 3020 20 25

[0017] The glasses of this invention can be ion exchanged usingconventional thermal salt bath techniques well known in the industry,see for example “Glass waveguides by ion exchange: a review” OpticalEngineering, Vol. 24, Number 2, pg 244-250 (1985). Glass PWD-85 wassuccessfully ion exchanged by employing such standard molten salt bathprocedures. Typical processing conditions were 30 minutes at atemperature of 180° C. with the glass placed in a salt bath preparedfrom 25 mole % NH₄NO₃ and 75 mole % AgNO₃. Resultant analysis indicatedthe presence of Ag₂O to depths of 10 to 14 μm and concentrationsexceeding 25 mass % at the glass surface. FIG. 1 shows a typical Ag₂Oprofile. The rate of ion exchange found is actually higher thanrequired. Exchange times of several hours would still be acceptable tothe industry.

[0018] One way to increase the ion exchange time is to reduce the Na2Ocontent in the glass. Reduction of Na₂O content in P₂O₅—WO₃—Na₂Ocompositions results in a blue coloration of produced glass at regionswhere laser light generation or amplification is generally desired, seeFIG. 2. This blue coloration is due to a valence change of W⁶⁺ to W⁵⁺(to even W³⁺, see for example, C. R. Bamford, Colour Generation andControl in Glass, Elsevier, pg 118 (1977)). At the same time, once theprobable mechanism was understood to be reduction of W, efforts to solvethe blue color problem included melts prepared where different batchingpatterns to adjust the melt redox condition to a more oxidizingcondition. Alternatively, a lower Na₂O content glass can be prepared bysubstituting some of the Na₂O by one or more other alkali that do notexchange as well for Ag₂O.

[0019] An alternative path to lower diffusion coefficient for Na inP₂O₅—WO₃—Na₂O glasses is to introduce glass modifiers that act as ionexchange barriers. Possible modifier additions include alkaline earths,B₂O₃, Sb₂O₃ and Ga₂O₃. Glasses prepared along these lines of reasoningare detailed in Table 3. TABLE 3 Additional P₂O₅—WO₃—Na₂O Glass MeltingPWD- PWD- PWD- PWD- PWD- PWD- PWD- PWD- PWD- PWD- PWD- PWD- PWD- Oxide124 125 127 128 129 130 131 132 133 134 135 136 20326 Bi₂O₃ 4 B₂O₃ 5 5 55 5 Na₂O 23 25 25 23 25 25 20 20 21 25 25 25 25 Er₂O₃ 0.3 0.28 0.29 0.290.28 0.29 0.3 0.15 0.32 0.15 0.15 0.6 0.6 Yb₂O₃ 0.29 0.28 0.29 0.15 0.150.15 Ga₂O₃ 5 5 5 5 5 Sb₂O₃ 5 BaO 2 2 WO₃ 55 50 50 55 50 50 55 55 55 5050 55 55 P₂O₅ 20 20 20 20 20 20 15 15 20 20 20 20 20

[0020] Tables 2 and 3 demonstrate a continual trend of rare earthcontent solubility limit, independent of the identity of the employedrare earth, to about ≦2×10²⁰ Ln/cm³. The Er and Er codoped with Ybglasses offer improved Er spectroscopic properties over state-of-the-artphosphate glasses such as IOG-1 (IOG-1 is the example glass in U.S. Pat.No. 5,334,559). The Yb and Nd doped glasses offer lasing action, forexample, PWD-122 and PWD-142 at roughly 1.02 um and 1.05 um,respectively. In addition, the broad width of emission in the glasseslends itself to the development of laser systems with short pulselengths in the range of less than 1 nsec.

[0021] Many of the example glasses discussed here have beencharacterized for other properties as disclosed in Table 5. TABLE 5Glass Properties Tungsten-Alkali-Phosphate Property PWD-78 PWD-85PWD-109 PWD-112 PWD-114 Units Density 4.85 4.57 4.767 4.863 4.867 g/ccCTE 155.8 157.8 10⁻⁷/° C. Tg 465.2 397 ° C. (DTA) Tg 459.4 463 ° C.(Dilatometer) T soft 525.9 450.3 526.4 ° C. Young's Modulus 52.82 48.05Gpa 2900 nm 0.93 1.1 1.62 cm⁻¹ 3000 nm 1.34 1.58 2.31 cm⁻¹ 3333 nm 1.882.18 3.07 cm⁻¹ Property PWD-124 PWD-125 PWD-127 PWD-133 PWD-134 PWD-135Units Density 4.925 4.66 4.77 5.197 4.663 4.765 g/cc CTE 158.3 160.5147.9 161.6 156.3 10⁻⁷/° C. Tg 452 439 451 457 443 ° C. (Dilatometer) Tsoft 530.6 ° C. 2900 nm 0.95 0.96 0.84 1.13 0.97 0.63 cm⁻¹ 3000 nm 1.351.09 0.97 1.52 1.05 0.74 cm⁻¹ 3333 nm 1.87 1.39 1.07 1.95 1.36 0.85 cm⁻¹

[0022]FIG. 3 shows the improvement in gain possible with Example PWD-112of the present invention in comparison to the prior art phosphate glassexemplified by glass IOG-1 when employed for C-band use.

[0023]FIG. 4 shows the improvement in gain possible with Example PWD-112of the present invention in comparison to the prior art phosphate glassexemplified by glass IOG-1 when employed in both the C-band and L-bandwavelength regions.

[0024] The entire disclosures of all applications, patents andpublications, cited herein are incorporated by reference herein.

[0025] The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

[0026] From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to, adapt it to various usages andconditions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1—Ag₂O Profile in Ion Exchanged PWD Glass.

[0028]FIG. 2—Transmission Curve and Photo of 2 mm Thick Sample of Melt.

[0029]FIG. 3—Normalized C-band gain improvement compared tostate-of-the-art phosphate glass.

[0030]FIG. 4—Normalized C-band and L-band gain improvement compared tostate-of-the-art phosphate glass.

What we claim is:
 1. A glass comprising >30-65 mole % WO₃, 5-35 mole %Na₂O, and 5-65 mole % P₂O₅, and doped with Ln₂O₃ up to the limit ofsolubility of Ln₂O₃ in the glass.
 2. A glass according to claim 1,comprising 50-60 mole % WO₃.
 3. A glass according to claim 1, comprisingabout 55 mole % WO₃.
 4. A glass according to claim 1, comprising 15-25mole % Na₂O.
 5. A glass according to claim 1, comprising 16-65 mole %P₂O₅.
 6. A glass according to claim L, comprising 20-30 mole % P₂O₅. 7.A glass according to claim 1, comprising 0.01-2.0 mole % Ln₂O₃.
 8. Aglass according to claim 1, wherein Ln₂O₃ is Er₂O₃ or Yb₂O₃ or a mixturethereof.
 9. A glass according to claim L, comprising 0.15-0.35 mole %Er₂O₃.
 10. A glass according to claim 1, comprising 0.28-0.32 mole %Er₂O₃.
 11. A glass according to claim L, comprising 0.1-1.4 mole %Yb₂O₃.
 12. A glass according to claim 1, comprising 0.3-1.2 mole %Yb₂O₃.
 13. A glass according to claim 1, further comprising MoO₃, Nb₂O₅,TiO₂, B₂O₃, Ga₂O₃, Sb₂O₃, BaO, Bi₂O₃, SnO₂, Y₂O₃, ZrO₂, TaO₅, In₂O₃, MO,or R₂O, wherein R is a mixture of a) Li or K and b) another alkalimetal, or R is a mixture of at least two elements selected from thegroup consisting of Li, Na, K, Rb, Cs, Ag, and Tl, and M is Mg, Ca, Sror Zn, or a mixture thereof, in a total amount of up to 15 mole %.
 14. Aglass according to claim 1, further comprising MoO₃, Nb₂O₅, TiO₂, B₂O₃,Ga₂O₃, Sb₂O₃, BaO, Bi₂O₃, SnO₂, Y₂O₃, ZrO₂, TaO₅, In₂O₃, Mo, or R₂₀,wherein R is Li or K without the presence of another alkali metal, or isa mixture of at least two elements selected from the group consisting ofLi, Na, K, Rb, Cs, Ag, and Tl, and M is Mg, Ca, Sr or Zn, or a mixturethereof, in a total amount of up to 15 mole %.
 15. A glass according toclaim 1, further comprising MoO₃, Nb₂O₅, TiO₂, B₂O₃, Ga₂O₃, Sb₂O₃, BaO,Bi₂O₃, SnO₂, Y₂O₃, ZrO₂, TaO₅, In₂O₃, Mo, or R₂₀, wherein R is a mixtureof a) Li or K and b) another alkali metal, or R is a mixture of at leasttwo elements selected from the group consisting of Li, Na, K, Rb, Cs,Ag, and Tl, and M is Mg, Ca, Sr or Zn, or a mixture thereof, in a totalamount of up to 15 mole %.
 16. A glass according to claim 1, furthercomprising MoO₃, Nb₂O₅, TiO₂, B₂O₃, Ga₂O₃, Sb₂O₃, BaO, Bi₂O₃, SnO₂,Y₂O₃, ZrO₂, TaO₅, In₂O₃, Mo, or R₂O, wherein R is Li or K without thepresence of another alkali metal, or is a mixture of at least twoelements selected from the group consisting of Li, Na, K, Rb, Cs, Ag,and Tl, and M is Mg, Ca, Sr or Zn, or a mixture thereof, in a totalamount of less than 10 mole %.
 17. A glass according to claim 1, furthercomprising MoO₃.
 18. A glass according to claim 1, further comprisingMoO₃ in an amount of about 10 mole %.
 19. A method for preparing a glassaccording to claim 1, comprising bringing into a composition >30-65 mole% WO₃, 5-35 mole % Na₂O, 5-65 mole % P₂O₅, and Ln₂O₃ up to the limit ofsolubility of Ln₂O₃ in the glass.
 20. A glass according to claim 1,which is in a bulk or fiber form.
 21. A laser generator or amplifiercontaining a glass according to claim
 1. 22. A method of generatingand/or amplifying optical laser radiation comprising using a glassaccording to claim 1 as an amplifying medium.
 23. A planar or fiberwaveguide structure comprising a glass according to claim
 1. 24. Anupconversion material, a nonlinear optical medium, an optical switch, asoldering or sealing material, or an encapsulating material over anelectronic component, comprising a glass according to claim
 1. 25. Aglass comprising >30-65 mole % WO₃, 5-35 mole % Na₂O, and 17-65 mole %P₂O₅, and doped with Ln₂O₃ up to the limit of solubility of Ln₂O₃ in theglass.
 26. A glass comprising >30-65 mole % WO₃, 5-35 mole % Na₂O, and5-65 mole % P₂O₅, and doped with Ln₂O₃ up to the limit of solubility ofLn₂O₃ in the glass, and wherein the glass contains an amount of tip to15 mole % of only one of Li₂O or K₂O without the presence of anotheralkali metal.
 27. A glass comprising >30-65 mole % WO₃, 5-35 mole %Na₂O, and 5-65 mole % P₂O₅, and doped with Ln₂O₃ up to the limit ofsolubility of Ln₂O₃ in the glass, and wherein the glass contains lessthan 10 mol % TeO₂.
 28. A glass according to claim 25 that contains lessthan 10 mol % TeO₂.
 29. A glass according to claim 26 that contains lessthan 10 mol % TeO₂.
 30. A laser glass comprising a glass lasing mediumand an exit surface for laser radiation, wherein said glass lasingmedium comprises >30-65 mole % WO₃, 5-35 mole % Na₂O, and 5-65 mole %P₂O₅, and doped with Ln₂O₃ up to the limit of solubility of Ln₂O₃ in theglass.
 31. A laser glass according to claim 30, comprising 16-65 mole %P₂O₅.
 32. A laser glass according to claim 30, comprising 20-25 mole %Na₂O.
 33. A laser glass according to claim 30 that contains less than 10mol % TeO₂.
 34. A hybrid structure of one or more materials comprisingone or more materials in which one or more of the materials is/are aglass according to claim
 1. 35. A hybrid structure according to claim34, which comprises a glass according to claim 1 bonded to another glassaccording to claim 1.